Current medium caliber automatic weapons such as the MK19 40 mm machinegun used by the U.S. military forces require relatively expensive training ammunition, and ranges adequate for firing these weapons. This results in the troops not receiving adequate training. Blank firing attachments for providing realistic training are well known for use with various small arms weapons, but until the present invention none have been suitable for the MK19. The present invention provides for adequate training by firing a blank cartridge which approximates the feel and noise of firing with normal ammunition. The blank cartridge is reloadable with an easily replaced propellant unit which can be applied by soldiers training in the field. Use of the blank training cartridge requires replacement of simple parts of the weapon to prevent accidental feeding of service ammunition while the blank firing attachment is installed.